Fastener driving tool

ABSTRACT

THE APPLICATION DISCLOSES A PNEUMATIC FASTENER DRIVING TOOL HAVING A BLADE ACTUATING PISTON WITH AN UPPER, GREATER DIAMETER PORTION SPACED FROM A LOWER, LESSER DIAMETER PORTION BY A RECESSED AREA FORMING AN AIR RETURN SPACE CONTINUOUSLY SUPPLIED WITH COMPRESSED AIR TO HOLD THE PISTON IN A NORMAL POSITION. THE DIFFERENT DIAMETER PORTIONS OF THE PISTON ARE SLIDABLE IN CORRESPONDING DIAMETER PORTIONS OF A CYLINDER, AND RESILIENT O-RING ON THE UPPER END OF THE LESSER DIAMETER PORTION OF THE CYLINDER SEALS AGAINST THE LESSER DIAMETER PISTON PORTION IN THE NORMAL POSITION OF THE PISTON TO SEAL THE AIR RETURN SPACE FROM THE LOWER END OF THE CYLINDER. THE LESSER DIAMETER PISTON PORTION CARRIES A NYLON BEARING WHICH GUIDES PISTON MOVEMENT BUT PERMITS AIR FROM THE RETURN SPACE TO BLOW BY INTO THE LOWER END OF THE CYLINDER WHEN THE PISTON IS MOVED OUT OF ITS NORMAL POSITION DURING A DRIVING AND RETURN STROKE.

March 23,; 1971 R, H, DOYL 3,572,211

FASTENER DRIVING Tool. v

Filed Jan. 1s, 1969 jai' ADM/JARD H. Done 777mm/ KUZZMMze/w/ /fa/N/m MWM /Jrme/JE Ys ILS. Cl. 91-417 6 Claims ABSTRACT' OF THE DISCLOSURE The application ldiscloses a pneumatic fastener driving tool having a blade actuating piston with an upper, greater diameter portion spaced from a lower, lesser diameter portion by a recessed area forming an air return space continuously supplied with compressed air to hold the piston in a normal position. The different diameter portions of the piston are slidable in corresponding `diameter portions of a cylinder, and a resilient O-ring on the upper end of the lesser diameter portion of the cylinder seals against the lesser diameter piston portion in the normal position of the piston to seal the air return space from the lower end of the cylinder. The lesser diameter piston portion carries a nylon bearing which guides piston movement but permits air from the return space to blow by into the lower end of the cylinder when the piston is moved out of its normal position during a driving and return stroke.

BACKGROUND OF THE INVENTION This invention relates to a pneumatic motor and, more particularly, to a pneumatic motor for a fastener driving tool including means for avoiding the ingestion of foreign material into the motor.

Pneumatic fastener driving tools such as those used to drive nails and staples frequently are operated in environments n which dirt, lint, and other foreign material is present. In tools using a two-diameter piston slidable in a two-diameter cylinder with a return air space located between the different diameter portions of the piston and supplied with compressed air for returning the piston to a normal position at the end of a stroke, there is a tendency for the lower or lesser diameter piston and cylinder portions to act as a syringe and draw air containing foreign objects into the cylinder. This results in excessive Wear of the resilient seals or O-rings on the piston. This problem is present, as an example, when the tools are used in fastening textiles or cloths because of the presence of lint in the air.

In the past, arrangements have been provided for preventing the syringe action of the piston and cylinder by insuring that the lower portion of the cylinder is held at atmospheric pressure or slightly thereabove during the return stroke of the piston. As an example, U.S. Pat. Nos. 3,106,136, 3,208,353, and 3,405,602 disclose arrangements for supplying compressed air from above the piston to the lower end of the cylinder to prevent the ingestion of foreign objects. These arrangements, however, sutfer from the disadvantages that some of the pistons `driving air is taken from the top of the piston during the driving stroke and that passages through the piston are required.

Another problem encountered, particularly with the two-diameter piston-cylinder tools is the difficulty of lubricating the walls of the lower cylinder portion. Tools of this type are lubricated by using an oiler in the inlet air line to place droplets of oil or other lubricant in suspension in the air stream. This adequately lubricates the upper cylinder walls. However, even though the piston return air contacts the walls of the lower cylinder, it has been determined that this air, for some reason, does nited States Patent ice not adequately lubricate the wall of the lower cylinder. The limited amount of air supplied to the lower cylinder through the pistons in the arrangements shown in the above-identified patents also fails to adequately lubricate the lower cylinder wall.

SUMMARY OF THE INVENTION In accordance with the invention, there is provided a pneumatic fastener driving tool having a closed housing forming a compressed air reservoir in which is mounted a cylinder having a greater diameter upper portion and a lesser diameter lower portion in which are slidably mounted corresponding greater and lesser diameter portions of a piston. The area between the different diameter portions of the piston is recessed to define in conjunction with the wall of the cylinder an air return space placed in continuous communication with the air reservoir delined by the tool housing. A fastener driving blade is secured to the lower end of the piston and is adapted when the piston is operated through a drive and return stroke to engage and set a fastener such as a nail supplied from a magazine assembly.

The reservoir in the tool is connected to a source of compressed air through a conventionl inlet line which includes an oiler that supplies droplets of oil or a lubricating medium which are carried in suspension in the come pressed air stream to provide means for lubricating the tool. The compressed air in the reservoir is continuously supplied to the air return space and by -virtue of the differential area of the upper and lower portions of the piston normally holds the piston in an upper position with the driver blade retracted. When compressed air is supplied to the exposed upper surface of the piston, as by opening a main valve between the reservoir and the top of the cylinder, the piston is driven downwardly in a driving stroke. By connecting the upper end of the piston to the atmosphere, the differential areas on the two piston portions are effective to return the piston to its normal position. During this return movement, a partial vacuum would be drawn in the lower portion of the cylinder resulting in the ingestion of foreign material that would have an adverse effect on the operation of the tool, particularly the resilient Oering usually provided to seal the interface between the lower piston portion and the engaged wall surface of the lower portion of the cylinder.

In accordance with the present invention, the lower portion of the piston carries a bearing member such as a ring or annular member formed of a material such as nylon which guides and provides a bearing surface for the lower portion of the piston as it moves through the driving and return strokes. This bearing member does not, however, seal the interface between the lower portion of the piston and the adjacent wall surface of the lower portion of the cylinder. In the normal position of lthe piston, a resilient O-ring carried on the inner wall of the cylinder adjacent its upper end provides a seal between the cylinder and the lesser diameter portion of the piston to seal off communication between the air return space and the lower end of the cylinder. However, as the piston moves downwardly away from its normal position, this seal is broken, and compressed air from the air return space is supplied to the lower end of the cylinder. This air maintains the lower end of the cylinder above or at atmospheric pressure during the return stroke of the piston to prevent the ingestion of foreign material. fIn addition, the bearing member on the lower or lesser diameter portion of the piston forces the compressed air from the air return space carrying the lubricating medium to flow in immediate proximity to the wall of the lower portion of the cylinder to lubricate this surface. This lubrication coupled with the fact that the nylon bearing member provides self-lubrication insures the provision of fully lubricated surfaces between the piston and cylinder at the lower end thereof and avoids damage to resilient O-rings previously encountered.

BRIEF DESCRIPTION OF THE DRAWINGS Many other objects and advantages of the present invention will become apparent from considering the following detailed description in conjunction with the drawings in which:

FIG. 1 is a fragmentary elevational view in partial section of a fastener driving tool embodying the present invention;

FIG. 2 is an enlarged sectional view taken along line 2-2 in FIG. 1;

FIG. 3 is an enlarged fragmentary view illustrating the cooperation between a fastener driving blade and a headed fastener as the fastener is being driven; and

FIG. 4 is an enlarged fragmentary sectional view illustrating a sealing and bearing arrangement provided for the lower portion of a piston included in the tool shown in FIG. l.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now more specifically to FIG. l of the drawings, therein is illustrated a fastener driving tool which embodies the present invention and which is indicated generally as 10. The fastener driving tool includes a housing 12 having a rearwardly extending handle 12A and defining a cavity or chamber forming a compressed air reservoir 14 which is open at one end. This open end is closed by a closure cap 16. A two-diameter cylinder indicated generally as 18 is disposed within the reservoir 14 and slidably receives a two-diameter piston indicated generally as 20. A fastener driving blade or element 22 is secured to the lower end of the piston and is adapted when the piston 2t) moves downwardly during a driving stroke to engage and drive a nail 24 supplied to a drive track 26 in a nosepiece 27 of the housing ,12 by a rearwardly extending magazine and nail strip feeding assembly indicated generally as 28. The assembly 28 which feeds the individual nails 24 to the drive track 26 on a flexible carrier strip 30 is shown and described in detail in the copending application of Allen R. Obergfell et al., Ser. No. 736,425, tiled June 12, 1968, which application is assigned to the same assignee as the present application.

To control the operation of the tool 18 and the reciprocation of the piston 20, there is provided a control valve assembly indicated generally as 32 which is actuated i by the depression of a trigger 34 when the tool is to be operated. If a safety or touch-trip linkage 36 is actuated by placing the lower end of the structure 27 against a workpiece 37, the control valve assembly 32 moves a main valve assembly (not shown) that normally closes the open upper end of the cylinder 18 to a displaced position so that compressed air enters the upper end of the cylinder 18 and drives the piston 2t) and the connected driving element 22 downwardly through a driving stroke. This driving stroke is terminated by engagement of the lower surface of the piston 2() with a resilient bumper 38 disposed in the lower end of the cylinder 18. At the end of the driving stroke, the control valve assembly 32 is provided with a control signal to cause the main valve (not shown) to again close the open upper end of the cylinder 18 and to connect the upper portion of the interior of the cylinder 18 to the atmosphere so that the piston 20 and the connected driving element 22 are returned to a normal condition. One suitable construction for the control system for controlling the movement of the piston and including the control valve assembly 32 is shown in the copending application of Allen R. Obergfell, Ser. No. 767,020, filed Aug. 26, 1968, now abandoned, which application is assigned to the same assignee as the present application.

Referring now more specifically to the construction of the piston 2t) and the cylinder 18, the cylinder 18 has a greater diameter upper portion 18A and a lesser diameter lower portion 18B in which are slidably mounted, respectively, a greater diameter upper portion 20A on the piston and a lesser diameter lower portion 20B. The piston 20 is recessed between the two portions 20A and 20B to provide an air return space 38 within the cylinder 18 which is placed in continuous communication with the reservoir 14 through a plurality of ports 40. Because of the greater area of the upper piston portion 20A compared with the exposed area of the lower piston portion 20B in the space 38, the compressed air continuously supplied through the ports 46 provides an upwardly directed biasing force which normally holds the piston 20 in the normal position illustrated in FIG. l of the drawings.

The interface between the piston portion 20A and the cylinder portion 18A is continuously sealed by a sealing member or resilient O-ring 42 carried on or within a recessed area on the upper piston portion 20A. In the normal position of the piston, the interface between the lower piston portion 20B and the adjacent wall of the lower cylinder portion 18B is sealed by a sealing member or resilient O-ring 44 carried in a recess on the inner wall of the cylinder 18. Thus, in the normal position of the piston 20, the air return space 38 is sealed at the upper and lower piston portions 20A and 20B.

To provide means for insuring a pressure of at least atmospheric pressure below the piston portion 20B in the lower portion 18B of the cylinder 18, and to provide both a bearing or guiding surface for the lower portion 20B of the piston 20 while insuring lubrication of the walls of the cylinder portion 18B, a circular or annular bearing member 46 preferably formed of a material such as nylon is mounted in a recess on the piston portion 28B below the area at which this piston portion is engaged by the O-ring 44. The bearing member 46 engages the walls of the cylinder portion 18B but does not provide a uid seal therewith.

Accordingly, when the piston 20 is moved downwardly at the beginning of a driving stroke, the piston portion 20B moves out of sealing engagement with the O-ring 44 as the piston moves downwardly, and compressed air bypasses or blows by the bearing member 46 through the interface between this bearing member and the adjacent portion of the wall of the cylinder portion 18B. During the downward movement of the piston 20, this air escapes to the atmosphere through spaced grooves or depressions 38A in the bumper 38 and a system of passageways to the atmosphere indicated generally as 48 at the lower end of the cylinder portion 18B. When the piston 20 is moved upwardly in its return stroke, compressed air from the return space 38 continues to blow by the bearing member 46 to the extent necessary to maintain the pressure below the piston portion 20B within the cylinder portion 18B at or slightly above atmospheric pressure. Thus, the retraction of piston 20 does not provide the effect of a syringe and draw foreign material into the piston portion 18B.

The use of the bearing member 46 on the lower or lesser diameter portion 2GB of the piston 20 also insures fully lubricated contact between the piston portion 20B and the adjacent walls of the cylinder portion 18B. More specifically, the compressed air supplied to the reservoir 18 is supplied with droplets of oil or a lubricating medium, and during both directions of movement of the piston 20 this lubrication bearing fluid passes through the interface between the bearing member 46 and the adjacent wall surface of the cylinder portion 13B. This brings the lubricating medium into direct engagement with the wall surfaces so that they are lubricated thereby. In additionI` the bearing member 46 is preferably formed of a self-lubricating material such as nylon which not only engages a fully lubricated wall surface of the cylinder portion 18B, but also is not subjected to the abrasive effect of foreign material since the ingestion thereof is prevented by maintaining atmospheric pressure or pressure slightly thereabove in that porton of the piston 18B which is disposed beneath the piston portion 20B. Further, since the air supplied to the lower end of the piston porton 18B is derived from the air return space 38, any loss of driving air from above the greater diameter piston portion 20A is avoided.

To prevent the bending of the upper end of the nail 24 and to prevent the lower end of the driving element 22 from skipping off of or bending an enlarged head 24A of the nail 24 so as to mar the workpiece 37, the lower end of the driver element 22 is provided with an inclined surface or structure 22A. This inclination is from 5 to 10 measured relative to the horizontal plane or the head 24A. of the nail 24 and faces toward the front of the tool 10 as contrasted with the rearwardly extending magazine assembly 28. Although the reason for this is not completely understood, the provision of the inclined surface 22A prevents the bending of the nail 24 during driving or sharp bending of the head 24A. In addition, it has also been determined that the provision of the inclined end surface 22A prevents the lower end of the drive element 22 from jumping off the head 24A or leaving contact with this head so that the lower end of the driving element 22 engages and mars the surface of the workpiece 37. The inclined surface 22A may provide a slight corresponding inclination in the head 24A of the driven nail 24, but this is not objectionable or apparent on visual inspection.

When the nail 24 is fed into the drive track 26 in a position immediately below the lower end of the driver 22, the upper flat impact receiving surface of the head 24A of the nail 24 is disposed generally perpendicular to the di rection of reciprocating movement of the driver 22. The head engaging surface 22A on the lower end of the driver 22 is inclined or raked at an angle of from 5 to 10 relative to the plane of the impact receiving surface on the head 24A facing outwardly toward the front of the tool |10, as contrasted with the rearward direction in which the handle 12A and the magazine assembly 28 extend. To insure that the alignment of the raked or inclined surface 22A relative to the structure of the tool 10 is maintained, the driver element 22 can be provided, for instance, with an aligning structure or surface such as a flattened wall 22B (FIG. 2) which cooperates with a similarly formed opening 50 in the upper portion of the structure 27 defining the drive track 26. Further, it has been determined that even though the angle of inclination is relatively small, the inclination of the flat surface 22A on the lower end of the driver 22 is maintained when the tool 10 has been used to drive over a million nails 24, even though some rounding of the sharp edges of the surface 22A has been detected.

What is claimed and desired to be secured by Letters Patent of the United States is:

1. In a fastener driving tool of the type having a cylinder with upper greater and lower lesser diameter portions in which a piston having corresponding greater and lesser diameter portions is slidably mounted, the piston being recessed between the greater and lesser diameter portions to provide a return air space, compressed air being supplied to the return air space between the different piston portions to return the piston from a displaced position in which the piston is primarily disposed in the lesser diameter portion of the cylinder to a normal position in which the lesser diameter piston portion is adjacent the upper end of the lesser diameter cylinder portion, the lesser diameter portion of the cylinder being closed to communication with the atmosphere except at its lower end so that the return air space is closed olf from the atmosphere when the piston is in both of its normal and displaced positions,

a resilient sealing element carried on the cylinder adjacent the upper end of the lesser diameter portion of the cylinder and providing a fluid seal with the lesser diameter piston portion when the piston is in said normal position,

and a bearing member carried on the lesser diameter portion of the piston at a point below the area on the lesser diameter piston portion engaged by the resilient seating element when the piston is in said normal position, said bearing member being constructed and arranged to provide a flow of air from the return air space to the lower end of the lesser diameter portion of the cylinder when the piston moves away from said normal position, the flow being limited by the bearing member to retain sufficient pressure in the return air space to return the piston from its displaced position to its normal position.

2. The fastener driving tool set forth in claim 1 in which the bearing member is an annular plastic element carried on the outer periphery of the lesser diameter piston portion.

3. A fastener driving tool of the type having a twodiameter piston slidably mounted in a two-diameter cylinder in which the top of the cylinder is selectively supplied with compressed air to drive the piston and connected to the atmosphere to permit the piston to be returned by compressed air supplied to the cylinder between the greater diameter upper portion and the lesser diameter lower portion of the piston, the lesser diameter portion of the cylinder being closed to the atmosphere except at its lower end, the combination of structure on the lesser diameter portion of the piston for supplying air from above the lesser diameter portion of the piston to the lower portion of the cylinder below the lesser diameter portion of the piston during the return of the piston in a quantity sufficient to maintain the lower portion of the cylinder below the lesser diameter portion of the piston at a pressure that is no less than atmospheric pres sure so as to prevent the ingestion of foreign material into the lower portion of the cylinder,

the structure including a bearing surface on the outer periphery of the lesser diameter portion of the piston which engages the adjacent surface of the cylinder to guide movement of the lesser diameter piston portion in the cylinder, said bearing surface being spaced from a fluid sealing contact with said adjacent surface of the cylinder to provide a flow of air from the area between the greater and lesser diameter portions of the piston to said lower portion of the cylinder below the lesser diameter portion of the piston, said spacing being such as to restrict said flow of air sufficiently to retain adequate air pressure between the greater and lesser diameter portions of the piston to effect piston return.

4. The fastener driving tool set forth in claim 3 in which the piston is held in a normal position between operating cycles,

and a resilient sealing ring is carried on the cylinder adjacent the upper end of the lower, lesser diameter portion for sealing the interface between the lesser diameter portion of the piston and the cylinder only when the piston is in said normal position.

5. In a fastener driving tool of the type having a piston with greater and lesser diameter portions slidably mounted in corresponding greater and lesser diameter portions of a cylinder, the different diameter portions of the piston and cylinder providing an air space, the lesser diameter portion of the cylinder being closed olf from communication with the atmosphere except at an end disposed beyond the lesser diameter portion of the piston,

7 means for supplying compressed air containing a lubri- 6. The fastener driving tool set forth in claim 5 in eating medium to the air space, which the piston has a normal position and which includes a bearing means carried on the lesser diameter portion means interposed between the lesser diameter portion of the piston and adapted to slidably engage the of the cylinder and piston for sealing said interface wall of the lesser diameter cylinder portion to guide when the piston is in said normal position.

movement of the piston, the bearing means providing 5 a restricted air ilow path through the interface be- References Cited tween the bearing means and the wall of the lesser UNITED STATES PATENTS diameter Cylinder pOItOD. O provide a OW 0f alf 892,194 6/1908 Stewart et al. 92 162 containing the lubricating medium through the inter- 10 2,698,604 1/1955 Edwards d 92 154 face, said interface limiting said flow of air t0 re- 3,084,672 .4/1963 Dalton g1 417A tain adequate air in said air space to effect piston 3,242,825 3/1966 Roosa 91-417A return, 3,301,139 1/ 1967 Garnkel 91-417A and control means for reciprocating the piston within the cylinder so that the air and lubricating medium 15 PAUL E- MASLOUSKY, Primary EXamllel' owing through the interface lubricate the surface of the lesser diameter portion of the cylinder as the US' Cl XR' piston is reciprocated. 91-404; 92-154, 158, 162 t 

